Handheld/mobile wireless devices often have limited capabilities compared to access points or other high-end devices, e.g., in terms of transmission power and beamforming capability. Furthermore, even if two wireless devices have high capabilities, the network geometry may be such that the path loss and/or shadowing in a link between them are very strong.
Hence, during a peer-to-peer communication between two mobile stations, these peer stations may not have enough resources to form a strong link for high-speed communication. This can be exacerbated in high-frequency links where severe path loss necessitates the use of directional communication.